Carguy1394
Active Member
Repair Pioneer A9 NSA.Any help or opinion is welcome
Repair Pioneer A9 NSA
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Carguy1394
Active Member
Well yes. I will write what I do while struggling with these amps. Maybe if I manage to repair them for someone then it will be useful. I have already learned a some about the circuit of this NSA amplifier. I'm not sure if my approach is right but practice will show. I also accept any advice except to give up. So if you want to help I appreciate a lot.
Carguy1394
Active Member
I keep trying to repair my A9 amplifiers because I am convinced that only those that have been unsuccessfully repaired or for parts can be bought from the Internet. I already proved this buying 4 pieces A9 all of them heavy beaten from repairing. I realized that the quality of these devices is due to the exceptional quality of the parts in them. Also, NSA design requires these fast transistors and diodes, which are increasingly difficult to find today.
On one of the amplifiers I repaired the power supply and took out the amplifier board with a drivers boards by extending all the wires so to be easy to measure the voltages on the board. This I plan to be my installation base with which to repair 3 amplifier boards with removed absolutely all transistors and connected to the driver boards also with removed drivers, as in the place of the final transistors I will solder resistors.All the connections are connected likes in the original condition .
My goal first step is to achieve symmetrical voltages and according to the specs / they are almost same with or without transistors/ in the holes of the removed transistors for the left and right channels. Because all three boards give about 50 volts to one of the ground of the connectors CN3 or CN4, which goes to the output of the ground of the speakers.
On one of the amplifiers I repaired the power supply and took out the amplifier board with a drivers boards by extending all the wires so to be easy to measure the voltages on the board. This I plan to be my installation base with which to repair 3 amplifier boards with removed absolutely all transistors and connected to the driver boards also with removed drivers, as in the place of the final transistors I will solder resistors.All the connections are connected likes in the original condition .
My goal first step is to achieve symmetrical voltages and according to the specs / they are almost same with or without transistors/ in the holes of the removed transistors for the left and right channels. Because all three boards give about 50 volts to one of the ground of the connectors CN3 or CN4, which goes to the output of the ground of the speakers.
Carguy1394
Active Member
I see that in the forum it is recommended to replace the diode 1S2473 with 512-1N4148. I have a question if some one can answer :
isn't 637-1N4151 or 78-1N4148 a better substitution in terms of speed if 0.2 A is not a problem compared to 0.3A. Here is a link to the data of the original which is with reverse recovery time 1.5nano sec:
https://datasheetspdf.com/pdf/529800/Rohm/1S2473/1
isn't 637-1N4151 or 78-1N4148 a better substitution in terms of speed if 0.2 A is not a problem compared to 0.3A. Here is a link to the data of the original which is with reverse recovery time 1.5nano sec:
https://datasheetspdf.com/pdf/529800/Rohm/1S2473/1
Carguy1394
Active Member
Or to ask the exact question: On the amplifier board of the A9 diodes D1-D4, D11-D18 marked in the repair catalog with a star as fast moving items, are the diode 1S2473 which is a fast diode with a time of 1.5 nanoseconds reverse recovery time, isn't it more good to be replaced with an almost as fast diode 637-1N4151 (2 n. second) or with 78-1N4148 (4 n, Sec.) instead of 512-1N4148 (8 n. sec?). Thank you
ItsGarand
Active Member
the * for "fast moving item" means at the time the service manual was printed, that particular item was popular or they received a lot of orders for it. I would suggest reading the Pioneer Tuning Fork guides that describe the parts that Pioneer used. The Tuning Fork series can be found here at AK or you can down load them from the inter-webs.
Carguy1394
Active Member
Ok for the notation for the stars, but this does not answer the main question which is: Which diode is the best substitute in general and in this case
Carguy1394
Active Member
This method of the sapper for now gives results. I don't even want to show pictures of what the A9 looks like with the boards removed from the box and connected with extended wires. I do not advise anyone to do this because the risk of causing a short circuit is huge. Do not do this at home! I do it at my own risk. The effect was astounding. After switching on through the DBT, of course, immediately the amplifier board started a solder to spark from a bad contact. There was no other way to find out. I had measured these cables with the multimeter 100 times. I re-soldered the solder which conducts 80V. and the parasitic voltage in the output mass disappeared. All voltages in the holes of the transistors turned out to be symmetrical for the left and right channel and the control values correspond. No voltage is applied to pin 14 of the power supply board. I also removed the power board There is something wrong there. I'll look for him tomorrow. Now I am one step forward and two steps back because I thought the power supply was good because it gives the control board the prescribed value for the boost board. And on the big capacitors everything was fine but without the load on the driver boards. Now I need to see why -80V is lost on pin 14. And on the plus terminal of the driver board came out 120V. I'm going back to the power board
Carguy1394
Active Member
Yes .Usually I am using Google speech to text recognition. Or I am writing on a laptop and the mouse pad is so sensitize that switching mi writing on random different places. So I apologies for this inconvenience to every one. Will be glad to correct this. Fill free to ask me what I post wrong and mi pleasure will be to explain.
Carguy1394
Active Member
The old tread tuning fork saga I abandoned because no one cared about it. That's why I opened a new tread and made a method by which to fix 4 amplifiers at once. I rely mainly on myself and my engineering experience. There are also a lot of valuable things in this forum. I read all the repairs of similar amplifiers led by Markthefixer and adapt them to my methods or vice versa. So this is a new venture and everything is different. If you want to be in class, what I do do not read the other trade, but only this one. There is also a conversation with another person, but he is ill and appears very rarely, so for now I am fighting alone. I am also in contact with my colleague, an electronics engineer who repairs radars, but he is also super busy. I describe all this with the sole purpose that if I can fix some of these amps there is something that will be useful for people like me. It is.
Carguy1394
Active Member
Bad connection of the power supply board was the reason for no voltage on the big caps. Solder all ripping montage connections and go fw
Carguy1394
Active Member
I already have +/- 60V on the power supply. Everything is connected without the transistors on the amplifier board. The voltages in the holes of the transistors are symmetrical for the left and right channels in places with an accuracy of 0.5V. Second stage - I mount the transistors on the amplifier board and the driver boards without power transistors. Everything is connected with wires outside the case of amplifier. I measure the voltages with DBT 72 watts. They seem normal for DBT. The symmetry of the driver voltages is ОК and has a tolerance of 0.05V. I'm experimenting with cheap internet drivers with the super close hFE. If everything is ok I will put the original ones. I am checking the voltage at both ends of the emitter resistance of the drivers R1 / L and R2 / R. I don't know if that should be my criteria for normal working drivers. Maybe not - because it seems to me that it is a balancing emitter resistance that equalizes the gain of the drivers. I think there should be a symmetrical voltage at both ends with opposite signs and their sum should be zero in the ideal case. However, the amount differs slightly from zero in both channels.
I run the amplifier at 120 V without DBT. After about 4 seconds, the relays are heard and the protection is switched off. The green light comes on. At the output of the speakers there is a voltage of 0.005V L and and 0.004V R. On the big caps is -/+ 60V also on the drivers boards on the red and orange cable. There is no hum in the headphones, no noise is heard, the indicators do not show any level. I will stop there before making a short circuit AGAIN. The next step is to measure the voltages of the soldering tracks of the final transistors. If they are ok, maybe it's better to solder 1K resistors as MTF said somewhere, or to simulate the final ones with two diodes each before to install the real power transistors? As MTF used to say about some other repair. I'm not very sure yet. I'll think tomorrow.
I run the amplifier at 120 V without DBT. After about 4 seconds, the relays are heard and the protection is switched off. The green light comes on. At the output of the speakers there is a voltage of 0.005V L and and 0.004V R. On the big caps is -/+ 60V also on the drivers boards on the red and orange cable. There is no hum in the headphones, no noise is heard, the indicators do not show any level. I will stop there before making a short circuit AGAIN. The next step is to measure the voltages of the soldering tracks of the final transistors. If they are ok, maybe it's better to solder 1K resistors as MTF said somewhere, or to simulate the final ones with two diodes each before to install the real power transistors? As MTF used to say about some other repair. I'm not very sure yet. I'll think tomorrow.
Carguy1394
Active Member
Here are the voltages . Something doesn't seem good to me.
On the drivers Q3 and Q4 which are 2SA985
come B -2.4V / E -2.4V and also this voltage goes to all final transistors 2SA1076 on the left and right channel. There is something wrong here. Somewhere Markthefixer ran a Spec1 repair but I can't find where it was right know. There he approved the driver board voltages before the PTs were installed. I'll look for it. But it seems to me that -2.9V and -2.4V is the wrong voltage in the driver boards. I'll have to track down where it's coming from. But that will happen after I come back from the lake, because there are barbecued ribs and Radeberger beer waiting for me! Cheers everyone and have a nice day!
On the drivers Q3 and Q4 which are 2SA985
come B -2.4V / E -2.4V and also this voltage goes to all final transistors 2SA1076 on the left and right channel. There is something wrong here. Somewhere Markthefixer ran a Spec1 repair but I can't find where it was right know. There he approved the driver board voltages before the PTs were installed. I'll look for it. But it seems to me that -2.9V and -2.4V is the wrong voltage in the driver boards. I'll have to track down where it's coming from. But that will happen after I come back from the lake, because there are barbecued ribs and Radeberger beer waiting for me! Cheers everyone and have a nice day!
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QSilver
Super Member
If you could try to condense what your trying to say to a set voltages or suspected wrong voltages, that would be helpful. Also remember that without referencing or providing a good quality schematic, These numbers and voltages might not mean much to anyone trying to help you.
What translation system are you using?
What language are you typing your answers in? Terms like "Sapper", I do not understand.
Soldering in 1K resistors might not be correct. It might be correct for one amplifier - that does not mean it is correct for another.
Voltages in the schematic are under specific conditions. If a voltage is not correct, it means there is too much current flow (low voltage), or too little current flow (higher voltage) There is a tolerance of all voltages because some will drift based on power conditions depending on where you live and use the equipment. (e.g. I have 253V here, 1 mile away, its 240V - 13V difference causes small differences in voltage in the amplifier)
What translation system are you using?
What language are you typing your answers in? Terms like "Sapper", I do not understand.
Soldering in 1K resistors might not be correct. It might be correct for one amplifier - that does not mean it is correct for another.
Voltages in the schematic are under specific conditions. If a voltage is not correct, it means there is too much current flow (low voltage), or too little current flow (higher voltage) There is a tolerance of all voltages because some will drift based on power conditions depending on where you live and use the equipment. (e.g. I have 253V here, 1 mile away, its 240V - 13V difference causes small differences in voltage in the amplifier)
ItsGarand
Active Member
The schematics for the older model can be found here: https://www.hifiengine.com/manual_library/pioneer/a-9.shtml
Perhaps you could state clearly and concisely the issue you are having with the amp you are trying to repair.
Perhaps you could state clearly and concisely the issue you are having with the amp you are trying to repair.
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Carguy1394
Active Member
A long time ago, I was the commander of a sapper platoon in the army, and that's where the word came from
You can google it : https://en.wikipedia.org/wiki/Sapper
Most of the time I am using speech to text recognition program and only some time I am typing on a laptop.
You are right about everything, but we learned Ohm's and Kirchhoff's law at school in the 8th grade. Here in Chicago the voltage is 120V and constantly fluctuates by several volts, and this also affects my meter, although it should be stabilized, but this zener KZL-140 can also give deviations or something else, of course. but I measure now 58V and then 55V, for example, on the PT's collectors. I offered you the A9 scheme twice and also sent you a link to the HiFi engine
I also have the complete scheme on paper, which I photographed in files, but I can only send it by email because it is about 250 Mb.
file:///C:/Users/a/Downloads/hfe_pioneer_a-9_service_en-1.pdf
On the picture I have posted (if it is clearly visible, of course) I have posted the measured voltages of the left and right channel driver boards. I have also written the numbers of the transistors and which transistor is which, BUT as I explained above for those who read carefully what I write, it is clearly explained that there are no transistors in the places of the PT. This means that the driver transistors are installed because I do not say that they are not there, and the PTs are not there because I say that they are not installed and I measure them on the tracks. In addition, I also wrote that I measure without DBT the 120V mains voltage for the USA. I can't imagine what I can write more clearly than that. So this is what I wrote -2.4V and -2.9V are the question. And should be this digit of voltage there?
Carguy1394
Active Member
Is this the one you are trying to repair?
Yes, this is it . By accident, I became the owner of 4 of them for repair. One is already almost OK so the rest 3. I have described everything in another thread. But it is so long and unsuccessful. And you better not read it because it ends without result with so many unnecessary things. At the time I didn't know how to dealing with the problem, Now I have the strategy mentioned at the beginning of this post. I just explained to QSilver what the word sapper is. I've moved all the boards out of the amp case and extended the connecting wires so everything is connected and works like it's in the amp. So I can measure everything on the board and make some conclusions. But it really takes sapper skills not to cause a short circuit. The diagrams I have already.
In short. 3 A9 amplifiers with one burnt channel each. The damage has reached the power-regulator board and the amplifier board. The PT and the drivers with the emitter transistors burned out on one of the channels. The predrivers and their diodes as well and the 100 ohm resistors are also burnt on the burnt channel. ALL three amps have the same damage and roughly the same burnt parts
The question is about the voltages I described above and post a picture of a sheet with a measurements.
Should I install the power transistors with this voltages measured on the driver boards on the place where the power transistor should be installed?
Pls read the explanation above the attached picture
But I'm going to finish my Scotch treatment now because I was going to get sunstroke at the lake today.
and until tomorrow because it's midnight here
Cheers!
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Carguy1394
Active Member
A long time ago, I was the commander of a sapper platoon in the army, and that's where the word came from
You can google it : https://en.wikipedia.org/wiki/Sapper
Most of the time I am using speech to text recognition program and only some time I am typing on a laptop.
You are right about everything, but we learned Ohm's and Kirchhoff's law at school in the 8th grade. Here in Chicago the voltage is 120V and constantly fluctuates by several volts, and this also affects my meter, although it should be stabilized, but this zener KZL-140 can also give deviations or something else, of course. but I measure now 58V and then 55V, for example, on the PT's collectors. I offered you the A9 scheme twice and also sent you a link to the HiFi engine
I also have the complete scheme on paper, which I photographed in files, but I can only send it by email because it is about 250 Mb.
file:///C:/Users/a/Downloads/hfe_pioneer_a-9_service_en-1.pdf
On the picture I have posted (if it is clearly visible, of course) I have posted the measured voltages of the left and right channel driver boards. I have also written the numbers of the transistors and which transistor is which, BUT as I explained above for those who read carefully what I write, it is clearly explained that there are no transistors in the places of the PT. This means that the driver transistors are installed because I do not say that they are not there, and the PTs are not there because I say that they are not installed and I measure them on the tracks. In addition, I also wrote that I measure without DBT the 120V mains voltage for the USA. I can't imagine what I can write more clearly than that. So this is what I wrote -2.4V and -2.9V are the question. And should be this digit of voltage there?
The question is about the voltages I described above and post a picture of a sheet with a measurements.
Should I install the power transistors with this voltages measured on the driver boards on the place where the power transistor should be installed?
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QSilver
Super Member
Misunderstood about what you meant with Sapper. Sorry!
Anyway. All your E (Emitter readings) will or should be ~0mV because with the Output Transistors/Power Transistors (PT), there is no active components past this point.
C or Collector readings should all be + OR - Approximately 60VDC. This voltage drifts with line voltage so these are all fine at +58V and -58V. You should have a POSITIVE voltage with a NPN (2SC) and a NEGATIVE voltage with a PNP (2SA). You do so thats all good.
The most important voltage here right now is the B or Base voltage. This is the turn on voltage for the transistors. A voltage above approximately 0.6V positive or negative with respect to the transistor polarity, will turn the transistor on. These voltages should be below 0.6V if the Bias circuits are all turned to minimum. However, if there is no current flow through the bias circuit these voltages will float up to a higher voltage. Remember what I said earlier? No current flow causes a voltage to rise and more current flow causes a voltage to fall.
What transistors are currently in the driver positions? None?
Have you replaced all diodes and transistors on the main amplifier board yet? A simple yes or no will suffice here.
Anyway. All your E (Emitter readings) will or should be ~0mV because with the Output Transistors/Power Transistors (PT), there is no active components past this point.
C or Collector readings should all be + OR - Approximately 60VDC. This voltage drifts with line voltage so these are all fine at +58V and -58V. You should have a POSITIVE voltage with a NPN (2SC) and a NEGATIVE voltage with a PNP (2SA). You do so thats all good.
The most important voltage here right now is the B or Base voltage. This is the turn on voltage for the transistors. A voltage above approximately 0.6V positive or negative with respect to the transistor polarity, will turn the transistor on. These voltages should be below 0.6V if the Bias circuits are all turned to minimum. However, if there is no current flow through the bias circuit these voltages will float up to a higher voltage. Remember what I said earlier? No current flow causes a voltage to rise and more current flow causes a voltage to fall.
What transistors are currently in the driver positions? None?
Have you replaced all diodes and transistors on the main amplifier board yet? A simple yes or no will suffice here.
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